1. Field of the Invention
The present invention relates to a nonreciprocal circuit device. More particularly, the present invention relates to a nonreciprocal circuit device such as an isolator or a circulator for use in a microwave communication apparatus, and to a communication apparatus using the isolator or circulator.
2. Description of the Related Art
Generally, the function of a lumped-constant type isolator is to pass a signal only in a transmitting direction and to eliminate the transmission of the signal in the reverse direction.
Recently, in mobile communication apparatus, cost-reduction has been strongly demanded as well as miniaturization and weight-reduction. In such a circumstance, miniaturization, weight-reduction and cost-reduction have also been demanded in an isolator.
A lumped-constant type isolator shown in FIG. 10 has been proposed to meet the above demand. The lumped-constant type isolator 11 comprises a terminal case 13 which is made of resin and disposed on a lower yoke 12. The lower yoke 12 is made of magnetic metal and comprises right and left side walls 12a and a bottom wall 12b. A center electrode assembly 14 is accommodated in the terminal case 13 and an upper yoke 15 made of magnetic metal is placed thereon. Inside the upper yoke 15, a permanent magnet 16 is disposed. The permanent magnet 16 applies a DC magnetic field to the center electrode assembly 14.
The center electrode assembly 14 comprises a microwave ferrite 20 and three center electrodes 21, 22 and 23 disposed on the microwave ferrite 20. The three center electrodes 21-23 cross each other at angles of 120 degrees in an electrically insulated state. Port sections P1, P2 and P3 at first ends of the three center electrodes 21-23 are bent vertically and a shield section 26 which is common to the other ends of the three center electrodes 21-23 is contacted to the lower surface of the ferrite 20. The common shield section 26 substantially covers the lower surface of the ferrite 20, and is connected to the bottom wall 12b of the lower yoke 12 through a window 13a of the terminal case 13.
Input/Output electrodes 31, 32 and ground terminals 33, 34 are insert molded in the terminal case 13. First ends of the Input/Output electrodes 31, 32 are exposed outside the side wall of the case 13, and the other ends thereof are exposed inside the side wall of the case 13, to thereby form Input/Output connecting sections 18a, 18b inside the case 13. Similarly, first ends of the ground terminals 33, 34 are exposed outside the side wall of the case 13, and the other ends thereof are exposed inside the side wall of the case 13, to thereby form ground connecting electrode sections 17a, 17b and 17c, 17d, respectively.
Each of the port sections P1-P3 of the center electrodes 21-23 is connected to a hot-side capacitor electrode 1 of one of matching capacitors C1, C2 and C3. A cold-side capacitor electrode 2 of each of the matching capacitors C1-C3 is connected to the ground connecting electrode sections 17a, 17b, 17c, 17d. One end of a termination resistor R is connected to the hot-side capacitor electrode 1 of the matching capacitor C3, and the other end thereof is connected to the ground connecting electrode section 17b. That is, the matching capacitor C3 and the termination resistor R are electrically connected in parallel between the port section P3 of the center electrode 23 and ground. Further, the port sections P1 and P2 are connected to the Input/Output connecting electrode sections 18a and 18b, respectively.
In the above conventional isolator 11, each of the matching capacitors C1-C3 must be inserted between one of the port sections P1-P3 and one of the ground connecting electrode sections 17a, 17c, 17d, respectively, while holding the capacitor in a vertical orientation. Further, it is necessary to connect the capacitor electrodes 1, 2 of the matching capacitors C1-C3 to the port sections P1-P3 and the ground connecting electrode sections 17a, 17c, 17d by soldering.
However, the isolator 11 has the problem that the process of inserting the matching capacitors C1-C3 between the port sections P1-P3 and the ground connecting electrode sections 17a, 17c, 17d requires much time and effort, because the matching capacitors C1-C3 are small in size and difficult to handle. Further, since the port sections P1-P3 of the center electrodes 21-23 must be bent vertically in one of the initial steps in the assembly process, it is possible for the solder connection between the port sections P1-P3 and the matching capacitors C1-C3 to become unstable because of variations in the bend angle of the port sections P1-P3. Moreover, it is possible for the solder to spill and cause a short-circuit between the hot-side capacitor electrodes 1 and the cold-side capacitor electrodes 2 of the matching capacitors C1-C3, resulting in a defective product.
To overcome the above described problems, preferred embodiments of the present invention provide a nonreciprocal circuit device and a communication apparatus having high reliability, including a matching capacitor which is easy to assemble.
One embodiment of the present invention provides a nonreciprocal circuit device, comprising: a permanent magnet; a ferrite to which a DC magnetic field is applied by the permanent magnet; a plurality of center electrodes extending from a first major surface of the ferrite to a second major surface of the ferrite via side surfaces of the ferrite; a ground plate disposed on the second major surface side of the ferrite and electrically connected to the plurality of center electrodes; a plurality of matching capacitors electrically connected between the ground plate and port sections of the plurality of center electrodes respectively; and at least one matching capacitor being disposed such that a major surface thereof forms an angle in a range of 60 degrees to 120 degrees with a major surface of the ferrite.
According to the above arrangement, the matching capacitors can be connected between the center electrodes and the ground plate assembled with the ferrite in an initial assembly step. Thus, it becomes possible to handle the matching capacitors integrally with the center electrodes, the ground plate and the ferrite, as one unit. Therefore, mounting the matching capacitors becomes easier.
Further, an insulator for preventing a short circuit may be provided in the vicinity of the portion of the ground plate at which the matching capacitor is connected and in the vicinity of the port section of the center electrode. This insulator prevents an undesirable solder bridge from being formed by spilled solder when the matching capacitor is soldered. By this, for example, a short-circuit between the hot-side capacitor electrode and the cold-side capacitor electrode of the matching capacitor can be prevented.
Further, a communication apparatus according to the present invention has a lower manufacturing cost and higher reliability because the apparatus is provided with a nonreciprocal circuit device having the above described arrangement.
Also disclosed is a method of assembling the nonreciprocal circuit device.